Two-dimensional sensor arrays

ABSTRACT

Sensors incorporating piezoresistive materials are described. One class of sensors includes piezoresistive material that is held or otherwise supported adjacent conductive traces on a substrate. Another class of sensors includes conductive traces formed directly on the piezoresistive material. Two-dimensional sensor arrays incorporating piezoresistive materials are also described.

RELATED APPLICATION DATA

The present application is a continuation of and claims priority under35 U.S.C. 120 to U.S. patent application Ser. No. 14/800,538 entitledTwo-Dimensional Sensor Arrays filed on Jul. 15, 2015 (Attorney DocketNo. BBOPP004X1C1), which is a continuation of U.S. patent applicationSer. No. 14/464,551 entitled Two-Dimensional Sensor Arrays filed on Aug.20, 2014 (Attorney Docket No. BBOPP004X1), which is acontinuation-in-part application of U.S. patent application Ser. No.14/299,976 entitled Piezoresistive Sensors and applications filed onJun. 9, 2014 (Attorney Docket No. BBOPP004). Both application Ser. No.14/464,551 and application Ser. No. 14/299,976 are also non-provisionalsof and claim priority under 35 U.S.C. 119(e) to U.S. Provisional PatentApplication No. 61/993,953 entitled Piezoresistive Sensors andapplications filed on May 15, 2014 (Attorney Docket No. BBOPP004P). Theentire disclosure of each of the above-mentioned applications isincorporated herein by reference for all purposes.

BACKGROUND

Demand is rapidly rising for technologies that bridge the gap betweenthe computing devices and the physical world. These interfaces typicallyrequire some form of sensor technology that translates information fromthe physical domain to the digital domain. The “Internet of Things”contemplates the use of sensors in a virtually limitless range ofapplications, for many of which conventional sensor technology is notwell suited.

SUMMARY

According to various implementations, sensors and applications ofsensors are provided. According to a particular class ofimplementations, a sensor includes a flexible piezoresistive substrateand two or more conductive traces formed directly on or otherwiseintegrated with the piezoresistive substrate.

According to some implementations, the sensor includes circuitryconfigured to receive one or more signals from the conductive traces,and to detect a touch event with reference to the one or more signals.According to some of these implementations, the circuitry is furtherconfigured to determine either or both of a location of the touch event,and a magnitude of force of the touch event.

According to some implementations, the piezoresistive substrate is apiezoresistive fabric. According to others, the piezoresistive substrateis a piezoresistive rubber.

According to some implementations, the conductive traces comprise aconductive ink printed on the piezoresistive substrate. According toothers, the conductive traces comprise conductive paint deposited on thepiezoresistive substrate.

According to some implementations, the conductive traces are formed onlyon one side of the piezoresistive substrate. According to others, theconductive traces are formed on two opposing sides of the piezoresistivesubstrate.

According to some implementations, an insulating material formed over afirst one of the conductive traces, wherein at least a portion of asecond one of the conductive traces is formed over the insulatingmaterial and the first conductive trace.

According to some implementations, the two or more conductive tracesinclude a first conductive trace characterized by a first conductivityand a second conductive trace characterized by a second conductivitylower than the first conductivity. The sensor further includes circuitryconfigured to drive one end of the second conductive trace with a firstsignal characterized by a first duty cycle, and to drive an opposing endof the second conductive trace with a second signal characterized by asecond duty cycle. The circuitry is further configured to receive amixed signal from the first conductive trace; the mixed signal includingcontributions from the first and second signals via the piezoresistivesubstrate. The circuitry is further configured to detect a location of atouch event along a first axis of the second conductive trace withreference to the contributions of the first and second signals to themixed signal.

According to some implementations, the conductive traces are arranged ina first parallel array of the conductive traces oriented in a firstdirection formed on one side of the piezoresistive substrate, and secondparallel array of the conductive traces oriented at 90 degrees to thefirst array formed an opposing side of the piezoresistive substrate. Thesensor includes circuitry configured to sequentially drive the firstarray of conductive traces, and to sequentially scan the second array ofconductive traces. The circuitry is further configured to determine alocation and a magnitude of force for each of one or more touch eventswith reference to signals received from the second array of conductivetraces.

According to some implementations, the conductive traces are arranged inquadrants, and the sensor includes circuitry configured to detect atouch event with reference to signals received from the conductivetraces of the quadrants. The circuitry is further configured todetermine a location of the touch event, a magnitude of force of thetouch event, a speed of motion of the touch event, and a direction ofmotion of the touch event.

According to some implementations, the conductive traces are arranged ina plurality of conductive trace groups. Each of the conductive tracegroups includes two or more of the conductive traces. The resistancebetween the conductive traces in each of the conductive trace groupsvaries with force applied to the piezoresistive substrate in a vicinityof the conductive trace group. The sensor includes circuitry configuredto receive one or more signals from each of the conductive trace groupsand generate control information in response thereto. The controlinformation being for controlling operation of one or more processes ordevices in communication with the circuitry.

According to some implementations, the piezoresistive substrate is oneor more pieces of piezoresistive fabric integrated with a cap forwearing on a human head. Each of the pieces of piezoresistive fabric hasan array of the conductive traces thereon. The sensor includes circuitryconfigured to detect a touch event with reference to signals receivedfrom the conductive traces. The circuitry is further configured todetermine a location of the touch event and a magnitude of force of thetouch event.

According to a particular class of implementations, a sensor arrayincludes a piezoresistive substrate. A first array of conductive tracesis formed on the piezoresistive substrate and aligned with a firstdimension of the sensor array. A second array of conductive traces isformed on the piezoresistive substrate and aligned with a seconddimension of the sensor array. The sensor array has associated circuitryconfigured to apply drive signals to the first array of conductivetraces, to receive detection signals from the second array of conductivetraces, and to determine one or more locations of one or morecorresponding touch events on a surface of the sensor array using thedrive and detection signals.

According to some implementations, the piezoresistive substratecomprises a flexible piezoresistive material.

According to some implementations, the first and second arrays ofconductive traces are formed on only one side of the piezoresistivesubstrate. According to other implementations, the first and secondarrays of conductive traces are formed on both sides of thepiezoresistive substrate.

According to some implementations, the conductive traces of the firstarray are substantially parallel to each other and oriented along thefirst dimension, and the conductive traces of the second array aresubstantially parallel to each other and oriented along the seconddimension; the first and second dimensions being substantiallyperpendicular to each other.

According to some implementations, the conductive traces of the firstarray are characterized by a first conductivity, and the conductivetraces of the second array are characterized by a second conductivityhigher than the first conductivity. The circuitry is further configuredto drive one end of a first conductive trace of the first array with afirst signal, and to drive an opposing end of the first conductive tracewith a second signal, and to receive a mixed signal from a secondconductive trace of the second array. The mixed signal includescontributions from the first and second signals via the piezoresistivesubstrate, and the circuitry is configured to determine a first locationof a first touch event along the first conductive trace with referenceto a first value representing the contributions of the first and secondsignals to the mixed signal.

According to some implementations, the circuitry is further configuredto determine one or more additional locations of one or more additionaltouch events along any of the conductive traces of the first array thatare substantially simultaneous with the first touch event with referenceto one or more additional values representing one or more additionalmixed signals received from one or more of the conductive traces of thesecond array.

According to some implementations, the circuitry is further configuredto determine the first location of the first touch event as being alongthe first conductive trace and between adjacent conductive traces of thesecond array. According to some implementations, the circuitry isconfigured to determine the first location of the first touch event withreference to an additional value representing an additional mixed signalreceived from an additional conductive trace of the second array.

According to some implementations, the circuitry is further configuredto determine a second location of second touch event along the firstconductive trace that is substantially simultaneous with the first touchevent with reference to the first value and an additional valuerepresenting an additional mixed signal received from an additionalconductive trace of the second array.

According to some implementations, the circuitry is further configuredto drive one end of a third conductive trace of the first array with thefirst signal, and to drive an opposing end of the third conductive tracewith a third signal. The mixed signal also includes additionalcontributions from the first signal and the third signal correspondingto a second touch event near the third conductive trace that issubstantially simultaneous with the first touch event. The circuitry isfurther configured to generate the first value with reference to theadditional contributions from the first and third signals correspondingto the second touch event.

According to some implementations, the circuitry is configured toresolve the first location of the first touch event to one of aplurality of discrete locations associated with the first conductivetrace on the surface of the sensor array.

According to some implementations, the circuitry is further configuredto determine a force value for each touch event representing a magnitudeof a force for the corresponding touch event. According to someimplementations, the circuitry is configured to determine the forcevalue for each touch event with reference to an amplitude of acorresponding one of the detection signals.

According to some implementations, each of the conductive traces of thefirst array coincides with each of the conductive traces of the secondarray, and the circuitry is further configured to generate a data setfor the sensor array with reference to the detection signals. The dataset includes a data value for each coincidence of one of the conductivetraces of the first array with one of the conductive traces of thesecond array. The circuitry is configured to determine the one or morelocations of the one or more corresponding touch events with referenceto the data set.

According to some implementations, the circuitry is further configuredto determine a first location of a first touch event near a firstcoincidence of a first conductive trace of the first array and a secondconductive trace of the second array by comparing the data valuecorresponding to the first coincidence to a threshold. According to someimplementations, the threshold is determined with reference to anaverage of the data values.

According to some implementations, the circuitry is configured to repeatgeneration of the data set resulting in a plurality of data sets, eachdata set representing a state of the sensor array for a correspondingperiod of time. The circuitry is configured to determine the one or morelocations of the one or more corresponding touch events with referenceto the plurality of data sets. According to some implementations, thecircuitry is configured to determine the one or more locations of theone or more corresponding touch events with reference to the pluralityof data sets by comparing corresponding data values in successive onesof the data sets.

According to some implementations, the circuitry is configured togenerate first and second data values for each coincidence of one of theconductive traces of the first array with one of the conductive tracesof the second array. The first data value represents a location of anynearby touch event along the corresponding conductive trace of the firstarray, and the second data value represents a force associated with thenearby touch event.

According to some implementations, the circuitry is configured todetermine a plurality of locations of a plurality of substantiallysimultaneous touch events on the surface of the sensor array using thedrive and detection signals.

According to some implementations, the circuitry is configured toresolve detected touch events to a plurality of discrete locations onthe surface of the sensor array.

According to some implementations, the array includes a plurality offorce focusing elements each of which is aligned with one of thediscrete locations. One or both of the form factor of the force focusingelements and the flexibility of the force focusing elements may becontrolled to achieve a corresponding dynamic range of the sensor array.The force focusing elements may be part of the piezoresistive substrate.Alternatively, the array may include an additional substrate adjacent toa combination of the first and second arrays of conductive traces andthe piezoresistive substrate. The force focusing elements may be formedon the additional substrate. According to some implementations, theforce focusing elements are convex features on the additional substrate.According to some implementations, the additional substrate is part ofan environmental protection enclosure for the combination of the firstand second arrays of conductive traces and the piezoresistive substrate.

According to some implementations, a first additional substrate isadjacent to a combination of the first and second arrays of conductivetraces and the piezoresistive substrate. The first additional substratehas a plurality of structural elements extending therefrom at leastpartially through the piezoresistive substrate in spaces between theconductive traces. The sensor array further includes a second additionalsubstrate adjacent to the combination of the first and second arrays ofconductive traces and the piezoresistive substrate on an opposite sideof the combination from the first additional substrate. According tosome implementations, the structural elements extend all of the waythrough the piezoresistive substrate and contact the second additionalsubstrate without force exerted on the surface of the sensor array.According to some implementations, the structural elements extend onlypart of the way through the piezoresistive substrate. According to someimplementations, the first and second additional substrates are part ofan environmental protection enclosure for the combination of the firstand second arrays of conductive traces and the piezoresistive substrate.

According to some implementations, the piezoresistive substrate includesa plurality of apertures, each of the apertures being aligned with aspace between the conductive traces of the first and second arrays.According to some implementations, an additional substrate is adjacentto a combination of the first and second arrays of conductive traces andthe piezoresistive substrate. The additional substrate has a pluralityof structural elements extending therefrom at least partially throughthe apertures of the piezoresistive substrate. According to someimplementations, the structural elements have a form factorcorresponding to a shape of the apertures.

According to some implementations, the conductive traces of the firstarray are resistive traces, and the circuitry is configured to energizeeach of the conductive traces of the first array by simultaneouslydriving opposing ends of the conductive trace with first and secondsignals, respectively, using a plurality of signal busses. Each signalbuss is connected to a plurality of the conductive traces of the firstarray. The opposing ends of each conductive trace of the first array areconnected to a unique pair of the busses. According to someimplementations, the conductive traces of the second array arecharacterized by substantially zero resistance, and at least some of thelocations at which the circuitry is configured to determine touch eventsare along corresponding ones of the conductive traces of the first arrayand between respective pairs of the conductive traces of the secondarray.

According to some implementations, the circuitry is configured toresolve detected touch events to a plurality of discrete locations onthe surface of the sensor array. The plurality of discrete locationsform an array of Y discrete locations along the first dimension by Xdiscrete locations along the second dimension. The first array ofconductive traces includes X conductive traces, and the second array ofconductive traces includes fewer than Y conductive traces. X and Y areintegers greater than zero.

According to some implementations, the circuitry is configured toresolve detected touch events to a plurality of discrete locations onthe surface of the sensor array. The plurality of discrete locationsform an array of Y discrete locations along the first dimension by Xdiscrete locations along the second dimension. The first array ofconductive traces includes X conductive traces. X and Y are integersgreater than zero. The sensor array further includes a plurality ofbusses by which the circuitry applies the drive signals to the firstarray of conductive traces, the plurality of busses including fewer thanX busses.

According to some implementations, each of the conductive traces of thefirst array coincides with each of the conductive traces of the secondarray. The sensor array further includes a trace pattern at eachcoincidence of one of the conductive traces of the first array with oneof the conductive traces of the second array. Each trace patternincludes a first trace extending from the corresponding conductive traceof the first array and a second trace extending from the correspondingconductive trace of the second array. The first and second traces havecomplementary shapes. According to some implementations, one or both ofthe shapes of the first and second traces and the distance between thefirst and second traces is controlled to achieve a corresponding dynamicrange of the sensor array. According to a particular implementation, thecomplementary shapes of the first and second traces of each tracepattern are a clover shape and a cruciform shape.

According to another class of implementations, a sensor array includes afirst array of conductive traces aligned with a first dimension of thesensor array, and a second array of conductive traces aligned with asecond dimension of the sensor array. Piezoresistive material isconfigured to provide electrical connectivity between the conductivetraces of the first and second arrays. The sensor array includes aplurality of force focusing elements each of which is aligned with oneof a plurality of discrete locations on a surface of the sensor array.The sensor array has associated circuitry configured to apply drivesignals to the first array of conductive traces, to receive detectionsignals from the second array of conductive traces, and to determine oneor more locations of one or more corresponding touch events on thesurface of the sensor array using the drive and detection signals. Thecircuitry is also configured to resolve detected touch events tocorresponding ones of the plurality of discrete locations.

According to various implementations, one or both of the form factor ofthe force focusing elements and the flexibility of the force focusingelements is controlled to achieve a corresponding dynamic range of thesensor array. In some implementations, the force focusing elements arepart of the piezoresistive material. In others, the sensor array mayinclude a substrate adjacent to a combination of the first and secondarrays of conductive traces and the piezoresistive material; the forcefocusing elements being formed on the substrate. The force focusingelements may be convex features on the substrate. The substrate may bepart of an environmental protection enclosure for the combination of thefirst and second arrays of conductive traces and the piezoresistivematerial.

According to some implementations, the sensor array includes a firstsubstrate adjacent to the combination of the first and second arrays ofconductive traces and the piezoresistive material on an opposite side ofthe combination from a second substrate. One of the first substrate orthe second substrate has a plurality of structural elements extendingtherefrom at least partially through the piezoresistive material inspaces between the conductive traces. In some implementations, thestructural elements extend all of the way through the piezoresistivematerial and contact the other of the first substrate or the secondsubstrate without force exerted on the surface of the sensor array. Inothers, the structural elements extend only part of the way through thepiezoresistive material. The first and second substrates may be part ofan environmental protection enclosure for the combination of the firstand second arrays of conductive traces and the piezoresistive material.

According to some implementations, the piezoresistive material includesa plurality of apertures each of which is aligned with a space betweenthe conductive traces of the first and second arrays. In someimplementations, the sensor array includes a first substrate adjacent tothe combination of the first and second arrays of conductive traces andthe piezoresistive material on an opposite side of the combination froma second substrate. One of the first substrate or the second substratehas a plurality of structural elements extending therefrom at leastpartially through the apertures of the piezoresistive substrate. Thestructural elements may have a form factor substantially conforming to ashape of the apertures.

According to some implementations, the piezoresistive material is aflexible piezoresistive material. In some implementations, the first andsecond arrays of conductive traces may be formed on the piezoresistivematerial; either on only one side of the piezoresistive material, or onboth sides of the piezoresistive material. In others, one or both of thefirst and second arrays of conductive traces may be formed on one ormore substrates adjacent to the piezoresistive material.

According to another class of implementations, a sensor array includes afirst array of conductive traces aligned with a first dimension of thesensor array. The conductive traces of the first array are characterizedby a first conductivity. The sensor array includes a second array ofconductive traces aligned with a second dimension of the sensor array.The conductive traces of the second array are characterized by a secondconductivity higher than the first conductivity. A piezoresistivematerial provides electrical connectivity between the conductive tracesof the first and second arrays. Associated circuitry is configured toapply drive signals to the first array of conductive traces, to receivedetection signals from the second array of conductive traces, and todetermine one or more locations of one or more corresponding touchevents on a surface of the sensor array using the drive and detectionsignals. The circuitry is further configured to drive one end of a firstconductive trace of the first array with a first signal, and to drive anopposing end of the first conductive trace with a second signal. Thecircuitry receives a mixed signal from a second conductive trace of thesecond array. The mixed signal includes contributions from the first andsecond signals via the piezoresistive material. The circuitry is furtherconfigured to determine a first location of a first touch event alongthe first conductive trace with reference to a first value representingthe contributions of the first and second signals to the mixed signal.

According to some implementations, the circuitry is further configuredto determine one or more additional locations of one or more additionaltouch events along any of the conductive traces of the first array thatare substantially simultaneous with the first touch event with referenceto one or more additional values representing one or more additionalmixed signals received from one or more of the conductive traces of thesecond array.

According to some implementations, the circuitry is further configuredto determine the first location of the first touch event as being alongthe first conductive trace and between adjacent conductive traces of thesecond array. According to some implementations, the circuitry isconfigured to determine the first location of the first touch event withreference to an additional value representing an additional mixed signalreceived from an additional conductive trace of the second array.

According to some implementations, the circuitry is further configuredto determine a second location of second touch event along the firstconductive trace that is substantially simultaneous with the first touchevent with reference to the first value and an additional valuerepresenting an additional mixed signal received from an additionalconductive trace of the second array.

According to some implementations, the circuitry is further configuredto drive one end of a third conductive trace of the first array with thefirst signal, and to drive an opposing end of the third conductive tracewith a third signal. The mixed signal also includes additionalcontributions from the first signal and the third signal correspondingto a second touch event near the third conductive trace that issubstantially simultaneous with the first touch event. The circuitry isfurther configured to generate the first value with reference to theadditional contributions from the first and third signals correspondingto the second touch event.

According to some implementations, the circuitry is configured toresolve the first location of the first touch event to one of aplurality of discrete locations associated with the first conductivetrace on the surface of the sensor array.

According to some implementations, the conductive traces of the firstarray are resistive traces, and the circuitry is configured to energizeeach of the conductive traces of the first array by simultaneouslydriving opposing ends of the conductive trace with first and secondsignals, respectively, using a plurality of signal busses. Each signalbuss is connected to a plurality of the conductive traces of the firstarray. The opposing ends of each conductive trace of the first array areconnected to a unique pair of the busses. According to someimplementations, the conductive traces of the second array arecharacterized by substantially zero resistance, and at least some of thelocations at which the circuitry is configured to determine touch eventsare along corresponding ones of the conductive traces of the first arrayand between respective pairs of the conductive traces of the secondarray.

According to some implementations, the circuitry is configured toresolve detected touch events to a plurality of discrete locations onthe surface of the sensor array. The plurality of discrete locationsform an array of Y discrete locations along the first dimension by Xdiscrete locations along the second dimension. The first array ofconductive traces includes X conductive traces, and the second array ofconductive traces includes fewer than Y conductive traces. X and Y areintegers greater than zero.

According to some implementations, the circuitry is configured toresolve detected touch events to a plurality of discrete locations onthe surface of the sensor array. The plurality of discrete locationsforms an array of Y discrete locations along the first dimension by Xdiscrete locations along the second dimension. The first array ofconductive traces includes X conductive traces. X and Y are integersgreater than zero. The sensor array further includes a plurality ofbusses by which the circuitry applies the drive signals to the firstarray of conductive traces. The plurality of busses includes fewer thanX busses.

According to some implementations, the piezoresistive material is aflexible piezoresistive substrate. According to some implementations,the first and second arrays of conductive traces are formed on theflexible piezoresistive substrate. According to some implementations,the first and second arrays of conductive traces are formed on only oneside of the flexible piezoresistive substrate. According to others, thefirst and second arrays of conductive traces are formed on both sides ofthe flexible piezoresistive substrate. According to someimplementations, one or both of the first and second arrays ofconductive traces are formed on one or more additional substratesadjacent to the flexible piezoresistive substrate.

As will be appreciated by those of skill in the art, variouscombinations of the foregoing features and functionalities are withinthe scope of this disclosure. A further understanding of the nature andadvantages of various implementations may be realized by reference tothe remaining portions of the specification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D illustrate a particular sensor configuration.

FIGS. 2A-2D illustrate another sensor configuration.

FIG. 3 illustrates yet another sensor configuration.

FIG. 4 illustrates still another sensor configuration.

FIG. 5 illustrates a further sensor configuration.

FIG. 6 illustrates a two-sided sensor array.

FIG. 7 illustrates another sensor configuration and a technique foracquiring sensor data.

FIG. 8 illustrates various sensor configurations.

FIG. 9 illustrates a hemispherical sensor array.

FIG. 10 illustrates a portion of a hemispherical sensor array.

FIG. 11 illustrates a portion of a hemispherical sensor array.

FIG. 12 illustrates another sensor configuration and a technique foracquiring sensor data.

FIG. 13 illustrates a test system for piezoresistive materials.

FIG. 14 illustrates a controller that employs a variety of sensorconfigurations.

FIGS. 15A and 15B are simplified representations of two-dimensionalsensor arrays.

FIG. 16 is another simplified representation of a two-dimensional sensorarray.

FIG. 17 illustrates examples of drive signals for use with thetwo-dimensional sensor array of FIG. 16.

FIG. 18 illustrates examples of a variety of mechanical features for usewith two-dimensional sensor array.

FIG. 19 includes cross-sectional views of two-dimensional sensor arrays.

FIG. 20 provides a representation of data sets for a two-dimensionalsensor array generated over time.

DETAILED DESCRIPTION

Sensors incorporating piezoresistive materials are described in thisdisclosure. Specific implementations are described below including thebest modes contemplated. Examples of these implementations areillustrated in the accompanying drawings. However, the scope of thisdisclosure is not limited to the described implementations. Rather, thisdisclosure is intended to cover alternatives, modifications, andequivalents of these implementations. In the following description,specific details are set forth in order to provide a thoroughunderstanding of the described implementations. Some implementations maybe practiced without some or all of these specific details. In addition,well known features may not have been described in detail to promoteclarity.

Piezoresistive materials include any of a class of materials thatexhibits a change in electrical resistance in response to mechanicalforce or pressure applied to the material. One class of sensors includespiezoresistive material that is held or otherwise supported (e.g.,within a silicone key or control pad) in proximity to conductive tracesarranged on a substrate (e.g., a printed circuit board (PCB)). Anotherclass of sensors includes conductive traces formed directly on orotherwise integrated with a flexible substrate of piezoresistivematerial, e.g., a piezoresistive fabric or other flexible material. Whenforce or pressure is applied to either type of sensor, the resistancebetween traces connected by the piezoresistive material changes in atime-varying manner that is representative of the applied force. Asignal representative of the magnitude of the applied force is generatedbased on the change in resistance. This signal is captured via theconductive traces (e.g., as a voltage or a current), digitized (e.g.,via an analog-to-digital converter), processed (e.g., by an associatedprocessor or controller or suitable control circuitry), and mapped(e.g., by the associated processor, controller, control circuitry, orother device or process) to a control function that may be used inconjunction with virtually any type of process, device, or system. Insome implementations, arrays of conductive traces having variousconfigurations are used to determine the location, direction, and/orvelocity of the applied force in one or more dimensions (e.g., inaddition to the magnitude of the force or pressure).

A particular class of implementations builds on designs described inU.S. patent application Ser. No. 12/904,657 entitled Foot-OperatedController, now U.S. Pat. No. 8,680,390, and U.S. patent applicationSer. No. 13/799,304 entitled Multi-Touch Pad Controller, published asU.S. Patent Publication No. 2013/0239787, the entire disclosures of bothof which are incorporated herein by reference for all purposes. In someof these implementations the piezoresistive material is held adjacent(e.g., in contact with or just off) the conductive traces in a flexiblekey or control pad structure constructed of, for example, silicone. Bycontrolling the geometry of the silicone, the pattern and density of theconductive traces, and the distance of the piezoresistive material fromthe trace pattern, a variety of sensors can be constructed that havevery different response curves and dynamic ranges that are appropriatefor a wide range of different applications. It should be noted that thefollowing sensor designs may employ any of the configurations andtechniques described in the attached disclosures in variouscombinations.

FIGS. 1A-1C illustrate a particular sensor configuration 100 useful forimplementing the keys of an electronic keyboard. The depicted sensorconfiguration is intended to be sensitive to a light touch, but alsohave a dynamic range that is sufficient to provide a significant rangeof expressiveness for its musician users. Two piezoresistive components102 and 104 allow the musician to rock key 106 forward and backward toachieve a variety of desired effects, e.g., note bending, vibrato, etc.

A cantilever structure 108 in silicone key 106 (a webbing element thatconnects the key to a surrounding framing structure and suspends the keywithin the structure) allows it to collapse evenly and easily, bringingpiezoresistive elements 102 and 104 into contact with the correspondingconductive trace patterns 110 and 112 on PCB 114 with very littlepressure, e.g., 30-50 grams. The silicone includes stops 115 that resistthe vertical travel of the key and define the placement ofpiezoresistive components 102 and 104. Stops 115 are configured toreduce the effect of higher magnitude forces on the sensor output. Theconductive trace patterns by which the change in resistance is measuredare configured as a star or asterisk 116 within a spoked circle 118. Thedensity of the trace pattern, the proximity of the piezoresistivecomponents to the conductive traces, and the configuration of thesilicone results in a response curve (FIG. 1D) in which only 30-40 gramsof pressure results in a significant drop in resistance. The x-axis ofthe curve represents kilograms of force and the y-axis represents alinearly scaled representation of the sensor's 7-bit analog-to-digitalconverter output. The curve flattens out after about 8-10 kg, butprovides sufficient dynamic range to allow a significant degree ofexpressiveness.

FIGS. 2A-2C illustrate another sensor configuration 200 intended tohandle a higher range of force than the sensor configuration of FIGS.1A-1C. The conductive traces are arranged in a concentric pattern ofrings 202 with the change in resistance being measured between adjacentrings. Given its trace pattern density, the spacing of piezoresistivematerial 204 from the conductive traces, and the overall mechanicalresistance of structure 206 to force, this sensor configuration doesn'tregister much of a response until about 5 kg of force is applied (FIG.2D). On the other hand, this configuration has useful dynamic range outpast 25 kg. Again, the x-axis of the curve represents kilograms of forceand the y-axis represents a linearly scaled representation of thesensor's 7-bit analog-to-digital converter output.

Even with careful attention paid to the various elements of the sensorconfiguration, the dynamic range of a sensor configuration is ultimatelylimited by the dynamic range of the piezoresistive material itself.According to a particular class of implementations, the range of thepiezoresistive material employed is about 40 dB (i.e., about 100:1).This may not be sufficient for some applications. Therefore, accordingto a particular class of implementations, the sensitivity of a sensorconfiguration is extended beyond the dynamic range of the piezoresistivematerial by including multiple piezoresistive components that are spacedat different distances from the conductive traces. According to thisapproach, the more distant piezoresistive component(s) “take over” whenthe closer piezoresistive component(s) run out of dynamic range. Anexample of one such sensor configuration is shown in FIG. 3.

In sensor 300 of FIG. 3, two distinct piezoresistive components 302 and304 are supported in a molded silicone structure 306 at differentdistances from corresponding patterns of conductive traces 308 and 310on a PCB 312. The piezoresistive components have a concentricconfiguration (when viewed along the z-axis) in which a circularpiezoresistive component is surrounded by an annular piezoresistivecomponent. The conductive traces corresponding to each of thepiezoresistive components are arranged as parallel traces in an areasimilar in shape to the corresponding piezoresistive component. Thechange in resistance for each set of parallel traces is measured betweenadjacent traces.

As the silicone in which piezoresistive components 302 and 304 areembedded is compressed, the closer annular component contacts thecorresponding conductive traces on the PCB first. As the silicone isfurther compressed, the more distant circular component then contactsits corresponding conductive traces on the PCB. In the depictedimplementation, the silicone and the distances of the piezoresistivecomponents from the PCB are constructed such that the more distantcomponent and the corresponding traces become active around where thecloser component and its traces begin to run out of dynamic range. Forexample, the closer piezoresistive component and the correspondingconductive traces might have a dynamic range covering 0 to about 50 kgof force while the more distant piezoresistive component and its tracesmight have a dynamic range from about 50 to about 100 kg.

It should be noted that the concentric arrangement of the piezoresistivecomponents and their corresponding trace patterns are merely one exampleof how multiple components may be configured to achieve a desireddynamic range for a sensor configuration. That is, implementations arecontemplated in which the piezoresistive components and theircorresponding trace patterns have different shapes and relativearrangements. Implementations are also contemplated in which there aremore than two piezoresistive components with corresponding tracepatterns. For example, an array might be arranged in a checkerboardpattern in which alternating piezoresistive components and theircorresponding trace patterns are configured to cover two or moredifferent parts of the overall dynamic range of the sensor.

Implementations are also contemplated in which the different dynamicranges associated with the different piezoresistive materials areachieved (at least in part) through variation in the shape,configuration, spacing, and/or conductivity of the different tracepatterns. For example, a closely-spaced, dense trace pattern might beused to cover a more sensitive portion of a dynamic range, while a morewidely-spaced, sparser trace pattern is used to cover a less sensitiveportion of the dynamic range. These types of variations may be done incombination with varying the spacing of the piezoresistive componentsfrom the trace patterns and/or the mechanical resistance to appliedforce of different areas of the sensor.

According to a particular implementation and as shown in FIG. 3, thesignals from the multiple piezoresistive components can be read using ashared signal line. In the depicted implementation, the conductivetraces corresponding to the closer piezoresistive component covering thelower part of the dynamic range are biased with a lower potential (e.g.,2.5 volts). That is, half of the traces are connected to the lowerpotential alternating with the other half of the traces being connectedto ground via a fixed resistance, as well as providing the output of thesensor (e.g., to an A-to-D converter via a multiplexer). The conductivetraces corresponding to the more distant piezoresistive componentcovering the higher part of the dynamic range are similarly biased witha higher potential (e.g., 5 volts). With this configuration, the dynamicrange associated with the closer piezoresistive component (e.g., 304) isrepresented by the range of 0-2.5 volts, while the dynamic rangeassociated with the more distant piezoresistive component (e.g., 302) isrepresented by the range of 2.5-5 volts on the same signal line.Reducing the number of signal lines required to acquire this sensor datais advantageous, particularly where there are multiple sensors fromwhich data are acquired.

According to a particular class of implementations, sensors may beimplemented using one or more arrays of driven or scanned conductivetraces alternating with conductive traces connected to a voltagereference, e.g., ground, through a resistor. Each array is overlaid witha corresponding piezoresistive component. The driven conductive tracesin each array are sequentially selected and activated, e.g., by raisingits voltage to a known level. When pressure is applied, the driventrace(s) at the point of contact are connected to the adjacent commontraces through the piezoresistive material. The voltage at the junctionof the common traces and the driven trace(s) is thereby raised. Theprocessor or controller driving the driven traces also sequentiallymeasures the corresponding signal levels to determine whether and wherea touch event occurs, and the magnitude of the pressure applied. Theprocessor or controller can also therefore detect the direction andspeed of the touch event along the array. As will be appreciated,because of the sequential selection and activation of the traces, suchconfigurations are capable of detecting multiple touch eventssubstantially simultaneously.

FIG. 4 shows a configuration of such a sensor 400 in which conductivetraces 402 and 404 are arranged in a linear array. FIG. 5 shows aconfiguration 500 in which the conductive traces 502-508 are arranged intwo parallel linear arrays. The sensor configurations shown in FIGS. 4and 5 are designed for use as a fader or slider control with anelongated rectangular key. The linear arrays of conductive traces foreach configuration are each aligned with a corresponding piezoresistivecomponent (406 or 510 and 512) supported at a distance from thecorresponding traces in a silicone structure (408 or 514). A cantileverstructure (410 or 516) in the silicone (i.e., the webbing element thatconnects and suspends a key part of the structure (412 or 518) to andwithin a framing part of the structure (414 or 520)) allows it tocollapse evenly and easily, bringing the piezoresistive components intocontact with the corresponding arrays with very little pressure, e.g.,30-50 grams. The silicone structure may include guides (416) forplacement of the piezoresistive components as well as stops (418) thatresist the vertical travel of the key. By having two arrays as shown inthe configuration of FIG. 5, the associated processor or controller candetermine not only the linear location, force, and direction of touchevents, but also lateral motion perpendicular to the arrays, e.g.,rocking left and right on the key.

According to another class of implementations, conductive traces areprinted, screened, deposited, or otherwise formed directly onto orintegrated with flexible piezoresistive material. As will beappreciated, this allows for the creation of a sensor or sensor arraythat fits any arbitrary shape or volume. The piezoresistive material maybe any of a variety of woven and non-woven fabrics having piezoresistiveproperties. And although reference may be made to piezoresistivefabrics, implementations are also contemplated in which thepiezoresistive material may be any of a variety of flexible materials(e.g., rubber, or a stretchable fabric such as spandex or open meshfabrics) having piezoresistive properties. The conductive traces may beformed using any of a variety of conductive inks or paints.Implementations are also contemplated in which the conductive traces areformed using any flexible conductive material that may be formed on theflexible piezoresistive material. It should therefore be understoodthat, while specific implementations are described with reference tospecific materials and techniques, the scope of this disclosure is notso limited.

Both one-sided and two-sided implementations are contemplated, e.g.,conductive traces can be printed on one or both sides of thepiezoresistive material. As will be understood, two-sidedimplementations may require some mechanism for connecting conductivetraces on one side of the piezoresistive material to those on the otherside. Some implementations use vias in which conductive ink or paint isflowed through the via to establish the connection. Alternatively, metalvias or rivets may make connections through the piezoresistive material.

Both single and double-sided implementations may use insulatingmaterials formed on the piezoresistive material and/or the conductivetraces. This allows for the stacking or layering of conductive tracesand signal lines, e.g., to allow the routing of signal line to isolatedstructures in a manner analogous to the different layers of a PCB.

Routing of signals on and off the piezoresistive material may beachieved in a variety of ways. A particular class of implementationsuses elastomeric connectors (e.g., ZEBRA® connectors) which alternateconductive and non-conductive rubber at a density typically an order ofmagnitude greater than the width of the conductive traces to which theyconnect (e.g., at the edge of the material). Alternatively, a circuitboard made of a flexible material (e.g., Kapton), or a bundle ofconductors may be riveted to the material. The use of rivets may alsoprovide mechanical reinforcement to the connection.

Matching conductive traces or pads on both the piezoresistive materialand the flexible circuit board can be made to face each. A layer ofconductive adhesive (e.g., a conductive epoxy such as Masterbond EP79from Masterbond, Inc. of Hackensack, N.J.) can be applied to one of thesurfaces and then mated to the other surface. The conductive traces orpads can also be held together with additional mechanical elements suchas a plastic sonic weld or rivets. If conductive rivets are used to makethe electrical connections to the conductive traces of thepiezoresistive material, the conductive adhesive may not be required.Conductive threads may also be used to connect the conductive traces ofthe piezoresistive material to an external assembly.

According to a particular class of implementations, the piezoresistivematerial is a pressure sensitive fabric manufactured by Eeonyx, Inc., ofPinole, Calif. The fabric includes conductive particles that arepolymerized to keep them suspended in the fabric. The base material is apolyester felt selected for uniformity in density and thickness as thispromotes greater uniformity in conductivity of the finishedpiezoresistive fabric. That is, the mechanical uniformity of the basematerial results in a more even distribution of conductive particleswhen a slurry containing the conductive particles is introduced. Thefabric may be woven. Alternatively, the fabric may be non-woven such as,for example, a calendared fabric e.g., fibers, bonded together bychemical, mechanical, heat or solvent treatment. Calendared material maypresent a smoother outer surface which promotes more accurate screeningof conductive inks than a non-calendared material.

The conductive particles in the fabric may be any of a wide variety ofmaterials including, for example, silver, copper, gold, aluminum,carbon, etc. Some implementations may employ carbon graphenes that areformed to grip the fabric. Suitable piezoresistive materials may befabricated using techniques described in U.S. Pat. No. 7,468,332 forElectroconductive Woven and Non-Woven Fabric issued on Dec. 23, 2008,the entire disclosure of which is incorporated herein by reference forall purposes. However, it should again be noted that any flexiblematerial that exhibits a change in resistance or conductivity whenpressure is applied to the material and/or on which conductive tracesmay be printed, screened, deposited, or otherwise formed will besuitable for implementation of sensors as described herein.

Conductive particles may be introduced to the fabric using a solution orslurry, the moisture from which is then removed. According to someimplementations, the way in which the moisture is removed from thefabric may also promote uniformity. For example, using an evenlydistributed array of vacuum heads or ports to pull the moisture from thefabric reduces the concentrations of conductive particles aroundindividual vacuum heads or ports. The vacuum heads or ports may bearranged in 1 or 2 dimensional arrays; the latter being analogized to areverse air hockey table, i.e., an array of vacuum ports which pull airin rather than push air out.

Implementations are also contemplated in which the uniformity of thepiezoresistive fabric is not necessarily very good. Such implementationsmay use multiple, closely-spaced sensors operating in parallel, theoutputs of which can be averaged to get more accurate and/or consistentreadings.

According to a particular class of implementations, conductive traceshaving varying levels of conductivity are formed on the piezoresistivematerial using conductive silicone-based inks manufactured by, forexample, E.I. du Pont de Nemours and Company (DuPont) of Wilmington,Del., and/or Creative Materials of Ayer, Mass. An example of aconductive ink suitable for implementing highly conductive traces foruse with various implementations is product number 125-19 from CreativeMaterials, a flexible, high temperature, electrically conductive ink.Examples of conductive inks for implementing lower conductivity tracesfor use with various implementations are product numbers 7102 and 7105from DuPont, both carbon conductive compositions. Examples of dielectricmaterials suitable for implementing insulators for use with variousimplementations are product numbers 5018 and 5036 from DuPont, a UVcurable dielectric and an encapsulant, respectively. These inks areflexible and durable and can handle creasing, washing, etc. The degreeof conductivity for different traces and applications is controlled bythe amount or concentration of conductive particles (e.g., silver,copper, aluminum, carbon, etc.) suspended in the silicone. These inkscan be screen printed or printed from an inkjet printer. Another classof implementations uses conductive paints (e.g., carbon particles mixedwith paint) such as those that are commonly used for EMI shielding andESD protection.

One example of a two-sided implementation is shown in FIG. 6 and has anarray 602 of parallel conductive traces oriented in one directionprinted on one side of the piezoresistive fabric, and another array 604oriented at 90 degrees to the first array printed on the other side ofthe fabric. This implementation takes advantage of the fact that thepiezoresistive fabric is conductive through its thickness (in additionto laterally and across its surface) to implement a pressure sensitiveX-Y matrix. By sequentially driving the array on one side of thepiezoresistive material and sequentially scanning the array on the otherside, both the position and force of a touch event on the array can bedetected. Again, because of the sequential selection and activation ofthe traces, such a configuration is capable of detecting multiple touchevents substantially simultaneously. As will be understood, theapplications for such a sensor array are virtually limitless.

As will be understood by those of skill in the art, a variety oftechniques may be employed to acquire data from sensors constructed asdescribed herein. Some of these techniques may involve a simplemeasurement of a change in resistance (as determined from a voltage orcurrent) between two conductive traces having the same or similarconductivity. However, for sensors having arrays that include manyconductive traces, this may require an unacceptable number of signallines to route signals both to and from the sensor array. Therefore,according to a particular class of implementations, conductive tracesformed on piezoresistive material and having different levels ofconductivity are driven and interrogated with signal patterns thatreduce the number of signal lines required to achieve sensorconfigurations that are sensitive to location, pressure, direction, andvelocity of applied force.

FIG. 7 illustrates an example of such an implementation intended toprovide functionality similar to the sensor of FIG. 5 but with fewersignal lines. Adjacent (in this case substantially parallel) conductivetraces are formed on piezoresistive fabric 700 with one (E) being highlyconductive, e.g., near-zero resistance, and the other (AB) being lessconductive, e.g., about 100 ohms from A to B if the resistance betweentraces AB and E without pressure is about 1K ohms. The less conductivetrace is driven at opposing ends by different signals A and B (e.g., byone or more signal generators). Pressure on the piezoresistive materialreduces the resistance between the two traces which, depending on thelocation, results in different contributions from signals A and Bmeasured in a mixed signal on the highly conductive trace E. The overallamplitude of the mixed signal also increases with pressure.

According to a particular class of implementations, signals A and B aredifferent pulse trains of the same amplitude; e.g., one at 1 kHz, onewith a 50% duty cycle, and the other at 500 Hz with a 75% duty cycle asshown in FIG. 7. The phases of the two pulse trains are synchronized toavoid zero volts being applied to the less conductive trace. Locationinformation can be derived from the mixed signal measured on E asfollows. The signal on E is sampled by an A/D converter (e.g.,oversampled by a factor of two or more relative to the frequency of theinputs). An inexpensive, general-purpose processor may be employed thatcan read up to 40 signals with up to 10-bits of resolution, and take500K samples per second. The same general processor may drive theconductive traces. Thus, arrays with large numbers of sensors may beconstructed relatively inexpensively.

The processor evaluates specific amplitudes at specific times that arecorrelated with the values of signals A and B at those times. Therelative contribution from each signal is determined by selectingclosely-spaced samples of the mixed signal at times when the respectivesignals are each known to have a particular value or characteristic,e.g., full amplitude. The ratio of those two measurements represents therelative contributions of each signal to the mixed signal that, in turn,can be mapped to a location between the end points of the AB trace. Thepressure or force of the touch event can be determined by measuring peakvalues of the sampled mixed signal. With this configuration, a pressuresensitive slider can be implemented with only 3 signal lines required todrive the traces and acquire the signal (as opposed to the many signallines associated with the linear array of traces in sensor configurationof FIG. 5.

According to a particular implementation shown in FIG. 7, a secondconductive trace CD runs parallel to trace E on the opposing side fromtrace AB. As with trace AB, the opposing ends of this additionalconductive trace are driven with signals C and D; each different fromthe other as well as signals A and B. As a result, the mixed signal ontrace E includes contributions from each of the four signals. This mixedsignal may be processed for one or both of the signal pairs in a mannersimilar to that described above to determine the location of a touchevent along the longitudinal axis of the array. The relative amplitudesof the two signal pairs (e.g., derived by measuring amplitudes for thecombination of signals A and B and the combination of signals C and D)represent the location of the touch event along the latitudinal axis ofthe array. This enables measuring of the location of the touch event intwo dimensions. This might enable, for example, the capture of asideways rocking motion of a finger on a key. As with the exampledescribed above, the pressure of the touch event may be determined bymeasuring peak values of the sampled mixed signal. In this way, an XYZsensor may implemented with five traces (with the Z axis beingrepresented by the force of the touch event).

FIG. 8 shows a variety of trace patterns formed on flexiblepiezoresistive material, e.g., conductive ink on piezoresistive fabric,for different applications. Trace pattern 802 implements a four-quadrantsensor that operates similarly to those described, for example, in U.S.Pat. No. 8,680,390 and U.S. Patent Publication No. 2013/0239787,incorporated herein by reference above. In addition to detecting theoccurrence and force of touch events, such a sensor may also beconfigured to determine the direction and velocity of motion over thequadrants including, for example, both linear and rotational motionrelative to the surface of the sensor. Trace patterns 803 (clover andcruciform configuration), 804, 806 and 808 implement sensors thatmeasure the occurrence and force of touch events with different responsecurves and dynamic ranges resulting from the different configurations.

Trace pattern 810 is used to illustrate both single and double-sidedimplementations that use either vias or rivets through thepiezoresistive material (e.g., configuration 812), insulating materialsformed over conductive traces (e.g., configuration 814), or both. Asdiscussed above, such mechanisms enable complex patterns of traces androuting of signals in a manner analogous to the different layers of aPCB.

FIG. 9 illustrates a sensor array 900 for inclusion in a helmet or skullcap worn on a human head, e.g., for measuring the force and location ofimpacts. Such an array might be suitable, for example, for capturingdata regarding contact events on sports helmets or other protective geardesigned to protect the human head. This information might be usefulduring the design and testing phases of such protective gear, as well asgathering data once in use. It should be noted that sensors located in acap that covers areas of the skull provide information about contactevents that actually reach the skull. This is to be contrasted with someexisting systems that instead measure the contact event to theprotective helmet. Each flap 902 is constructed from a flexiblepiezoresistive material 904 with a pattern of conductive traces formedon the material, e.g., conductive ink printed on piezoresistive fabric.As with the traces of FIG. 7, some of the traces 906 are highlyconductive and alternate with traces 908 having lower conductivity.

Like trace AB of FIG. 7, traces 908 on each flap are driven at opposingends with signals having the same amplitude and different duty cycles.The same pair of signals may be used for all of the flaps. These signalsare routed to the opposing ends of traces 908 from the center of thearray via traces 910 and 912. As can be seen, trace 912 on each flapcrosses over traces 906 from which trace 912 is insulated, e.g., frominsulators (not shown) printed or formed over the underlying conductivetraces.

Each of the signals on traces 906 is routed to the center of the arrayand represents the mixing of the signals on adjacent traces 908. Thelocation and magnitude of touch events along longitudinal axes of thetraces (e.g., the radial coordinate from the center of the array) may bedetermined from the mixed signal as described above with reference toFIG. 7. The angular coordinate may be determined from the conductivetrace 906 that registers the touch event.

An alternative implementation of the flap for such a sensor arraysimilar to the one depicted in FIG. 9 is shown in FIG. 10. Flap 1002includes an alternating pattern of highly conductive traces 1006 andtraces 1008 and 1009, both of which are characterized by a lowerconductivity than traces 1006. However, instead of driving each of thelower conductivity traces with the same signal pair as described abovewith reference to FIG. 9, traces 1008 are driven with one signal pair(using trace 1010) and traces 1009 are driven with another (using traces1011). This is analogous to the addition of the second conductive traceCD described above with reference to FIG. 7. That is, the mixed signalspresent on each of traces 1006 can be processed as described above withreference to the configuration of FIG. 7 to determine the relativecontributions from the 4 signals driving adjacent traces 1008 and 1009,and therefore the location of an applied force in two dimensions, e.g.,along the longitudinal axes of the traces (the radial coordinate fromthe center of the array), and the latitudinal axes of the traces (theangular coordinate relative to the center of the array). The magnitudeof the applied force may also be determined as described above withreference to FIG. 7.

FIG. 11 illustrates a pattern of conductive traces 1102 on a flap 1104that may be on the other side of the flap from the trace patterns ofFIG. 9 or 10. Traces 1102 may be used in conjunction with the techniquesdescribed above to disambiguate between multiple simultaneous touchevents. For example, as discussed above, the mixed signals on traces1006 of FIG. 10 include contributions from adjacent traces 1108 and 1109as affected by the location and magnitude of an applied force or touchevent. However, if there were two simultaneous touch events on the sameflap, there would be ambiguity as to the locations of the events as themixing of the resulting signals would, in effect, perform a kind ofaveraging that would result in a reading that doesn't accuratelyrepresent the location of either event. Traces 1102 on the other side ofthe flaps may be configured to address this issue.

According to a particular implementation in which multiple flaps 1104are configured as shown in FIG. 9, a roughly hemispherical shape may beformed by bringing the long edges of the flaps together. Traces 1102 canbe connected to corresponding traces on adjacent flaps to form somethinganalogous to latitude lines around the hemisphere. Signals on each ofthese traces can be read (e.g., by an analog-to-digital converter (ADC)and an associated processor) to identify the places of activity on theopposite side of the fabric. For example if two pressure points arealong the same longitudinal trace on the other side of the fabric (e.g.,traces 1006) they may not be distinguishable. However, by examining thelatitudinal traces it can be determined where the points of contact arebased upon increased signal level present. Locations between thelatitudinal traces can be determined using relative signal strength.

As will be appreciated, the sampling rate of the latitudinal conductorsmay be sufficiently fast to detect multiple touch events at differentlatitudes substantially simultaneously. As will also be appreciated, ifthe traces 1102 on all of the flaps are connected as described, theinformation derived from these traces will only give a latitude for eachof the multiple touch events. However, this can be combined withinformation derived from traces on the other side of the flaps (e.g., asdiscussed above with reference to FIGS. 9 and 10) to determine thelongitudinal (e.g., east to west) coordinates of the events. In analternative implementation, traces 1102 on each flap may be processedindependently of the other flaps with the introduction of additionalsignal lines.

As mentioned above, the description of specific implementations hereinis intended to provide illustrative examples rather than limit the scopeof this disclosure. And although two classes of sensors have beendescribed herein, it should be understood that at least some of thetechniques and configurations described may be employed by either classof sensor. For example, the technique for driving and reading conductivetraces described above with reference to FIG. 7 is not limited toimplementations in which the conductive traces are formed on thepiezoresistive material. That is, the same principle may be applied tothe class of sensors in which piezoresistive material is supported(e.g., within a silicone key or control pad) adjacent conductive tracesthat are arranged on a substrate (e.g., a printed circuit board (PCB))rather than formed directly on or otherwise integrated with thepiezoresistive material. An example of such an implementation isillustrated in FIG. 12.

In the depicted implementation, trace E (which may be, for example,copper) is formed on PCB 1202 with two adjacent and parallel traces ABand CD (which may be, for example, printed ink resistors). Theresistance of trace E is near zero. For some applications, theresistance of traces AB and CD may be about 10% of the relaxed surfaceresistance of piezoresistive material 1204 over the distance betweenthose traces and trace E. Piezoresistive material 1204 is held adjacentthe three traces in a compressible structure 1206 (which may be, forexample, silicone). Piezoresistive material 1204 may be held at adistance from the traces or in contact with them.

As described above with reference to FIG. 7, four unique signals A, B, Cand D drive the corresponding ends of traces AB and CD. The resultingmixed signal on trace E may then be processed to determine the location,direction, velocity and force of a touch event on the surface ofstructure 1206.

For implementations that employ arrays of sensors and/or in which themagnitude of applied forces captured by sensors is important, theuniformity of the piezoresistive material can be critical. Therefore, aclass of test systems is provided that is configured to measure changesin resistance of a piezoresistive material at a number of closely spacedlocations. According to a particular subclass of test systems, an arrayof conductive traces is provided on a substantially rigid substrate suchas, for example, a printed circuit board (PCB). A sheet ofpiezoresistive material (e.g., a piezoresistive fabric as describedherein) to be tested is placed over the PCB in contact with theconductive traces, and pairs of the conductive traces are sequentiallyactivated such that the signals representative of the resistance of thepiezoresistive material are captured at an array of locations (e.g., byassociated circuitry on the PCB). By introducing known forces on thepiezoresistive material, the response of the piezoresistive material maybe characterized over its surface and/or volume, thus yielding test datarepresenting how uniformly the material behaves in response to appliedforce.

As will be appreciated, such information would be extremely useful formanufacturers of piezoresistive materials in designing and evaluatingnew materials as well as classifying products with regard to theiruniformity characteristics. Such information would also be useful todesigners of systems incorporating such materials (e.g., sensor systems)in that they will be able to select materials that have a level ofuniformity that is appropriate for their particular application.

An example of such a test system 1300 is shown in FIG. 13. Pairs ofinterlaced conductive traces 1302 and 1304 are formed on a PCB toprovide an array of 256 locations at which the resistance of a sheet ofpiezoresistive material placed in contact with the array (not shown) maybe measured. As will be appreciated the number of locations, thearrangement of the array, and the configuration of the conductive tracesmay vary significantly (e.g., see examples described above) fordifferent implementations depending on a number of factors such as, forexample, the dynamic range required, the shape, size, and/orconstruction of the piezoresistive material to be tested, etc. TheSimplified Block Diagram included in FIG. 13 illustrates the connectionand control of each pair of traces. Trace 1302 is connected to ground(GND). Trace 1304 is pulled up to a bias voltage (VBIAS) of 3.3 voltsvia a variable impedance and is also the trace by which the resistancemeasurement of the material under test at that location of the array ismade.

Control circuitry 1306 (which may include, for example, a centralprocessing unit (CPU) and associated circuitry) sequentially reads thesignals at each of traces 1304 in the array by controlling multiplexers1308. The measurements are digitized and serialized and transmitted to acomputing device, e.g., a desktop or laptop computer, a tablet, a smartphone, etc. (not shown), via USB port 1310. As will be appreciated,similar conversion and processing circuitry may be used with any of thesensor configurations described herein. As force is exerted on apiezoresistive material under test in contact with a particular pair oftraces, the resistance of the material (represented by variable resistor1312) changes, and the resulting signal is captured by control circuitry1306. According to some implementations, additional structures may beformed on the PCB as a counterbalance to the conductive traces to bettermaintain the flatness of the PCB. These might be, for example,non-conductive traces or additional conductive traces that have noelectrical connections.

It will be appreciated that sensors and sensor arrays designed asdescribed in this disclosure may be employed in a very broad and diverserange of applications in addition to those described. One example ofsuch an application is a controller 1400 for a smart phone or a digitalmedia player as shown in FIG. 14. Controller 1400 may be implementedwith an underlying piezoresistive substrate 1402 with conductive tracespatterns 1404-1418 formed directly on or otherwise integrated with thesubstrate to implement sensors that provide different types of controls.The trace patterns are aligned with a particular icon representing thecontrol on an overlying substrate 1422 with which a user interacts(i.e., icons 1424-1438). Alternatively, trace patterns 1404-1418 may beformed on the opposite side of the same substrate from icons 1424-1438.The substrate(s) from which controller 1400 is constructed may be apiezoresistive fabric that may be incorporated, for example, in articlesof clothing, e.g., in the sleeve of a shirt or jacket.

As described elsewhere herein, when pressure is applied to one of thecontrols, a resulting signal may be digitized and mapped by associatedprocessing circuitry (e.g., multiplexer 1442, A-D converter 1443, andprocessor 1444) to a control function associated with a connecteddevice, e.g., the smart phone or media player (not shown) via, forexample, a USB or Bluetooth connection. As will be appreciated, similarconversion and processing circuitry may be employed with any of thesensor configurations described herein.

In the depicted implementation, trace pattern 1404 corresponds to icon1424 and implements a button control that allows the user to answer orterminate calls on his smart phone. Trace pattern 1406 corresponds toicon 1426 and implements a slider (such as the one described above withreference to FIG. 7) for volume control of, for example, a media player.Trace pattern 1408 corresponds to icon 1428 and implements afour-quadrant sensor that may be used for navigation of, for example,set lists, track queues, etc. Trace pattern 1410 corresponds to icon1430 and implements an enable/disable control by which controller 1400may be enabled and disabled. Trace patterns 1412-1418 correspond toicons 1432-1438, respectively, and implement various media playercontrols such as, for example, play, pause, stop, record, skip forward,skip back, forward and reverse high-speed playback, etc. As will beappreciated, this is merely one example of a wide variety of controllersand control functions that may be implemented in this manner.

According to a particular implementation, an insulating layer 1446 maybe printed or deposited on piezoresistive substrate 1402 before any oftrace patterns 1404-1418. As can be seen, openings in insulating layer1446 line up with the portions of the trace patterns intended toimplement the corresponding control functions. These portions of thetrace patterns are therefore printed or deposited directly on theunderlying piezoresistive substrate. By contrast, the conductive tracesthat connect these portions of the trace patterns to the edge of thepiezoresistive substrate for routing to the processing circuitry areprinted or deposited on insulating layer 1446. This will significantlyreduce crosstalk noise between these conductors relative to an approachin which they are also printed on the piezoresistive substrate.

Two-dimensional sensor arrays incorporating piezoresistive materials aredescribed in this disclosure. Specific implementations are describedbelow including the best modes contemplated. Examples of theseimplementations are illustrated in the accompanying drawings. However,the scope of this disclosure is not limited to the describedimplementations. Rather, this disclosure is intended to coveralternatives, modifications, and equivalents of these implementations.In the following description, specific details are set forth in order toprovide a thorough understanding of the described implementations. Someimplementations may be practiced without some or all of these specificdetails. In addition, well known features may not have been described indetail to promote clarity.

As discussed above, piezoresistive materials include any of a class ofmaterials that exhibits a change in electrical resistance in response tomechanical force or pressure applied to the material. A signalrepresentative of the magnitude of the applied force is generated basedon the change in resistance. This signal is captured via conductivetraces (e.g., as a voltage or a current with the piezoresistive materialas part of a divider circuit), digitized (e.g., via an analog-to-digitalconverter), processed (e.g., by an associated processor or controller orsuitable control circuitry), and mapped (e.g., by the associatedprocessor, controller, control circuitry, or a connected computingsystem) to a control function that may be used in conjunction withvirtually any type of process, device, or system.

FIG. 15A shows an example of a two-dimensional sensor array 1500 thatincludes a set of substantially parallel conductive traces 1502 orientedin one direction, and another set of substantially parallel conductivetraces 1504 oriented at about 90 degrees to the first set of traces.Traces 1502 and traces 1504 are electrically connected via apiezoresistive material (not shown for clarity). The traces and thepiezoresistive material may be positioned relative to each other in anumber of ways. For example, the piezoresistive material may be a fabricor other flexible substrate and the traces may be formed on thepiezoresistive material on opposite sides of the material. In anotherexample, the piezoresistive material might be sandwiched between twosubstrates on which the traces are formed or of which they are a part.In yet another example, both arrays of traces may be on the same side ofa piezoresistive substrate (formed either on the piezoresistive materialor separately from the piezoresistive material on or as part of anadjacent substrate) with insulation between the traces where theyintersect or coincide. Additional substrates that are adjacent thepiezoresistive material may also be fabric or other flexible materials.In implementations in which traces are formed on or part of one or moresuch substrates, the piezoresistive material may be coupled (e.g.,laminated) to the additional substrate(s) to form a multilayerstructure. Other suitable variations are within the scope of thisdisclosure.

By sequentially driving the traces of one set (e.g., using processor(s)1506, digital-to-analog converter 1508, and demultiplexer 1510), andsequentially scanning the traces of the other (e.g., using multiplexer1512, analog-to-digital converter 1514, and processor(s) 1506), both theposition and force of a touch event on the array can be detected. Andbecause of the sequential selection and activation of the traces, such aconfiguration is capable of detecting multiple touch eventssubstantially simultaneously. As will be understood, the applicationsfor such sensor arrays are virtually limitless.

FIG. 15B shows another example of a two-dimensional sensor array 1550that includes a set of substantially parallel conductive traces 1552oriented in one direction, and another set of substantially parallelconductive traces 1554 oriented at about 90 degrees to the first set oftraces. Sensor trace patterns 1556 are provided near the intersectionsof the horizontal and vertical traces; each pattern including a trace1558 connected to one of the vertical traces 1552, and a trace 1560connected to one of the horizontal traces 1554. The depicted exampleemploys a cruciform shape for trace 1560 and a clover shape for trace1558 that provides a significant area in which the two conductive tracesof the pattern are in close proximity to each other. As will beappreciated, the shapes of traces 1558 and 1560 and the distance(s)between them may be controlled to achieve a desired sensitivity (dynamicrange) for a given application. Examples of other traces patterns thatmay be suitable for particular applications (e.g., 1556-1 through1556-4) are shown. A variety of other configurations are within thescope of this disclosure.

Traces 1552 and 1558 are electrically connected with traces 1554 and1560 via a piezoresistive material (not shown for clarity). According tosome implementations of sensor array 150, the arrays of parallel tracesand the trace patterns are formed on one side of the piezoresistivematerial (either on the piezoresistive material or on a substrate thatis adjacent the piezoresistive material). In such implementationsinsulating material 1562 is provided at the intersections of theparallel traces 1552 and 1554 to insulate these traces from each other.However, it should be understood that, as with sensor array 1500,implementations are contemplated in which the traces of the respectivearrays are disposed on opposite sides of intervening piezoresistivematerial (e.g., traces 1552 and 1558 on one side of the material andtraces 1554 and 1560 on the other).

Sensor array 1550 has associated circuitry 1564 (which may be similar tothe circuitry shown in FIG. 15A) configured to apply drive signals toone set of conductive traces and to receive detection signals from theother. As discussed above with reference to sensor array 1500,sequential selection and activation of the traces by circuitry 1564enables detection of the position and force of a touch event on thearray, as well as the detection of multiple simultaneous touch events.

According to some implementations, the signal quality for touch eventson two-dimensional arrays such as arrays 1500 and 1550 may be improvedby connecting other traces in the array to a known potential (e.g.,ground) when a signal from a particular trace is being read (rather thanleaving them floating). This may reduce contributions from touch eventsassociated with the other vertical traces.

According to a particular class of implementations, conductive tracesare printed, screened, deposited, or otherwise formed onto flexiblepiezoresistive material. As discussed above, this allows for thecreation of a sensor array that fits any arbitrary shape or volume. Thepiezoresistive material may be any of a variety of woven and non-wovenfabrics having piezoresistive properties. Implementations are alsocontemplated in which the piezoresistive material may be any of avariety of flexible materials (e.g., rubber, or a stretchable fabricsuch as spandex or open mesh fabrics) having piezoresistive properties.The conductive traces may be arranged in a variety of ways depending onthe shape or volume to which the array is designed to conform. Forexample, the rectilinear configurations shown in FIGS. 15A and 15B maybe suitable for substantially flat implementations, while varyingdegrees of curvature of the traces and/or shaping of the overall shapeof the array may be desired for arrays conforming to other types ofsurfaces or shapes. According to some implementations, only portions ofan array might be used to enable the folding or rolling up of the arrayinto a desired form factor, e.g., if the upper right hand corner ofarray 1550 is removed, the remainder of the array could be rolled into aconical shape. Other such Euclidean transformations to achieve differentshapes and form factors are within the scope of this disclosure.

The traces may be formed using any of a variety of conductive inks orpaints. Implementations are also contemplated in which the conductivetraces are formed using any flexible conductive material that may beformed on the flexible piezoresistive material. It should therefore beunderstood that, while specific implementations are described withreference to specific materials and techniques, the scope of thisdisclosure is not so limited.

Both one-sided and two-side implementations are contemplated, e.g.,conductive traces can be printed on one or both sides of thepiezoresistive material. As will be understood, two-sidedimplementations may require some mechanism for connecting conductivetraces on one side of the piezoresistive material to those on the otherside. Some implementations may use vias in which conductive ink or paintis flowed through the via to establish the connection. Alternatively,metal vias or rivets may make connections through the piezoresistivematerial.

Both single and double-sided implementations may use insulatingmaterials formed over the piezoresistive material and/or the conductivetraces. This allows for the stacking or layering of conductive tracesand signal lines, e.g., to allow the routing of signal line to isolatedstructures in a manner analogous to the different layers of a PCB.

Routing of signals on and off the piezoresistive material may beachieved in a variety of ways. A particular class of implementationsuses elastomeric connectors (e.g., ZEBRA® connectors) which alternateconductive and non-conductive rubber at a density typically an order ofmagnitude greater than the width of the conductive traces to which theyconnect (e.g., at the edge of the piezoresistive material).Alternatively, a circuit board made of a flexible material (e.g.,Kapton), or a bundle of conductors may be riveted to the piezoresistivematerial. The use of rivets may also provide mechanical reinforcement tothe connection.

Matching conductive traces or pads on both the piezoresistive materialand the flexible circuit board can be made to face each. A layer ofconductive adhesive (e.g., a conductive epoxy such as Masterbond EP79from Masterbond, Inc. of Hackensack, N.J.) can be applied to one of thesurfaces and then mated to the other surface. The conductive traces orpads can also be held together with additional mechanical elements suchas a plastic sonic weld or rivets. If conductive rivets are used to makethe electrical connections to the conductive traces of thepiezoresistive material, the conductive adhesive may not be required.Conductive threads may also be used to connect the conductive traces ofthe piezoresistive material to an external assembly.

According to a some implementations, the piezoresistive material is apressure sensitive fabric manufactured by Eeonyx, Inc., of Pinole,Calif. The fabric includes conductive particles that are polymerized tokeep them suspended in the fabric. The base material is a polyester feltselected for uniformity in density and thickness as this promotesgreater uniformity in conductivity of the finished piezoresistivefabric. That is, the mechanical uniformity of the base material resultsin a more even distribution of conductive particles when a slurrycontaining the conductive particles is introduced. The fabric may bewoven. Alternatively, the fabric may be non-woven such as, for example,a calendared fabric e.g., fibers, bonded together by chemical,mechanical, heat or solvent treatment. Calendared material may present asmoother outer surface which promotes more accurate screening ofconductive inks than a non-calendared material.

The conductive particles in the fabric may be any of a wide variety ofmaterials including, for example, silver, copper, gold, aluminum,carbon, etc. Some implementations may employ carbon graphenes that areformed to grip the fabric. Piezoresistive materials may be fabricatedusing techniques described in U.S. Pat. No. 7,468,332 forElectroconductive Woven and Non-Woven Fabric issued on Dec. 23, 2008,the entire disclosure of which is incorporated herein by reference forall purposes. However, it should again be noted that any flexiblematerial that exhibits a change in resistance or conductivity whenpressure is applied to the material and on which conductive traces maybe printed, screened, deposited, or otherwise formed will be suitablefor implementation of sensor arrays as described herein.

According to a particular class of implementations, conductive traceshaving varying levels of conductivity are formed on the piezoresistivematerial using conductive silicone-based inks manufactured by, forexample, E.I. du Pont de Nemours and Company (DuPont) of Wilmington,Del., and/or Creative Materials of Ayer, Mass. An example of aconductive ink suitable for implementing highly conductive traces foruse with various implementations is product number 125-19 from CreativeMaterials, a flexible, high temperature, electrically conductive ink.Examples of conductive inks for implementing lower conductivity tracesfor use with various implementations are product numbers 7102 and 7105from DuPont, both carbon conductive compositions. Examples of dielectricmaterials suitable for implementing insulators for use with variousimplementations are product numbers 5018 and 5036 from DuPont, a UVcurable dielectric and an encapsulant, respectively. These inks areflexible and durable and can handle creasing, washing, etc. The degreeof conductivity for different traces and applications is controlled bythe amount or concentration of conductive particles (e.g., silver,copper, aluminum, carbon, etc.) suspended in the silicone. These inkscan be screen printed or printed from an inkjet printer. Another classof implementations uses conductive paints (e.g., carbon particles mixedwith paint) such as those that are commonly used for EMI shielding andESD protection.

The dynamic range of a two-dimensional sensor array implemented asdescribed herein may be manipulated through the use of a variety ofmechanical structures that may be included in or on any of the layers,substrates, or components of the array. Such structures may be flexible(e.g., silicone) components or features, the characteristics of which(e.g., shape, size, height, flexibility, number, placement, etc.) may bemanipulated to provide resistance to applied physical forces such that adesired dynamic range of the sensors is achieved. Some examples of suchstructures are described below with reference to FIG. 18. A wide varietyof other structures and components suitable for achieving a desiredsensitivity or dynamic range are within the scope of the disclosure.

As will be understood by those of skill in the art, a variety oftechniques may be employed to acquire data from sensors constructed asdescribed herein. Some of these techniques may involve a simplemeasurement of a change in resistance (as determined from a voltage orcurrent measurement) between two coinciding conductive traces having thesame or similar conductivity. However, for sensors having arrays thatinclude many conductive traces, this may require an unacceptable numberof signal lines to route signals both to and from the sensor array. Forexample, for the implementation of FIG. 15A having X traces 1504 and Ytraces 1502, the number of signal lines to the associated circuitrywould be X+Y. As will be understood, for very large arrays this maybecome difficult to implement. Therefore, according to a particularclass of implementations, conductive traces formed on piezoresistivematerial and having different levels of conductivity are driven andinterrogated with signal patterns that reduce the number of signal linesrequired to achieve sensor configurations that are sensitive tolocation, pressure, direction, and velocity of applied force.

FIG. 16 illustrates a particular implementation of a two-dimensionalsensor array 1600 that includes an array of parallel traces that arehighly conductive (e.g., near zero resistance) oriented in a firstdirection (vertically in the figure), and an array of parallel tracesthat are less conductive (e.g., about 500 to 1000 ohms each from end toend) oriented in a second direction (horizontally in the figure).Electrical connections between the traces are made via a piezoresistivematerial (not shown for clarity). As with the implementation describedabove with reference to FIGS. 15A and 15B, the traces and thepiezoresistive material may be positioned relative to each other in avariety of ways. Further, the conductive traces may be configured toconform to a particular surface or volume. So, although theimplementation of FIG. 16 illustrates a rectilinear array of traces thatare formed on opposite sides of a piezoresistive substrate, the scope ofthis disclosure is not so limited.

Drive signals generated by processor(s) 1602 are transmitted to thehorizontal traces via digital-to-analog converter 1604, de-multiplexer1606, and busses 1-4 and A-D. Each horizontal trace is designated by thepair of busses to which it is connected, i.e., the top horizontal tracein FIG. 16 is trace 1A, the next trace down is trace 2B, and so on. Notwo horizontal traces are connected to the same pair of busses. Signalsare received by processor(s) 1602 from vertical traces e-i viamultiplexer 1608, and analog-to-digital converter 1610. The resolutionof the array along the vertical axis is determined by the number andspacing of the horizontal traces. That is, the location of a touch eventalong this axis is determined by the location of the horizontal tracefor which it detected. However, as will be discussed, the resolutionalong the horizontal axis is greater than what is possible with thedepicted number and spacing of the vertical traces using conventionaltechniques.

In addition, as will be appreciated from the figure, the number ofsignal lines that must be routed to and from array 1600 is many fewerthan what is required for conventional arrays of comparable resolution.That is, a two-dimensional array typically has one signal line for eachhorizontal and each vertical channel, e.g., requiring X+Y signal linesto be routed off the array. By contrast, in the example illustrated inFIG. 16, array 1600 requires only 8 signal lines for 16 horizontaltraces, and only 5 signal lines for vertical traces that provide aresolution along the horizontal axis that would require many morevertical traces in a conventional array. This may be achieved asfollows.

In operation, each horizontal trace is energized in succession bysimultaneously driving the opposing ends of the trace with primarydetection signals S1 and S2 (shown in FIG. 17). While each horizontaltrace is energized, signals are read from the vertical traces insuccession. The force of a touch event on the piezoresistive materialreduces the resistance between intersecting traces near the touch pointwhich, depending on its location along the horizontal trace, results indifferent contributions from signals S1 and S2 measured in a mixedsignal on the highly conductive vertical trace. The overall amplitude ofthe mixed signal represents the magnitude of the force. By determiningthe relative contributions of S1 and S2 to the mixed signal a horizontallocation for the touch point may be determined.

According to a particular implementation and as illustrated in FIG. 17,primary detection signals S1 and S2 are different pulse trains of thesame amplitude but with different duty cycles (e.g., S1 at 1 kHz with a50% duty cycle, and S2 at 500 Hz with a 75% duty cycle), with the phasesof the two pulse trains synchronized as shown. Location information maybe derived from the mixed signal measured on the vertical conductivetrace as follows. The signal on the vertical trace is sampled by A/Dconverter 1610 (e.g., oversampled by a factor of two or more relative tothe frequency of the inputs). For processor(s) 1602, an inexpensive,general-purpose processor may be employed that can read up to 40 signalswith up to 10-bits of resolution, and take 500K samples per second. Thesame general processor may drive the conductive traces. As will beappreciated, having the same processor generate the signals and performthe A/D conversion simplifies timing of samples to coincide with changesof the drive states. It also reduces the overall space or volume takenup by these components and keeps costs down. Thus, large arrays may beconstructed relatively inexpensively. However, it should also beunderstood that implementations are contemplated in which differentprocessors may perform these functions. More generally and as will beunderstood by those of skill in the art, a wide variety of suitableprocessors, controllers, computing devices, logic devices and othersuitable circuitry may be adapted to control the sensors and sensorarrays described herein. Therefore, reference to specific circuitry ordevices should not be used to limit the scope of this disclosure.

According to some implementations and as shown in FIG. 18, the verticaltraces go through a multiplexer 1818 and into an inverting operationalamplifier 1820 that represents a virtual ground reference. As a result,the signal (e.g., a current) measured on any one of the vertical traceswill experience the lowest impedance to a ground reference and beaccurately representative of any nearby touch events in thatcontributions from more remote touch events on the array have a muchhigher resistive path and are dominated by the contributions from localevents.

The processor evaluates specific amplitudes at specific times that arecorrelated with the values of signals S1 and S2 at those times. Therelative contribution from each signal is determined by selectingclosely-spaced samples of the mixed signal at times when the respectivesignals are each known to have a particular value or characteristic,e.g., full amplitude. The ratio of those two measurements represents therelative contributions of each signal to the mixed signal that, in turn,can be mapped to a location between the end points of the trace.Examples of ratios of the contributions of signals S1 and S2representing different touch points along the horizontal axis are shownin FIG. 16, e.g., 75/25 corresponding to touch point TP-1, 67/33corresponding to touch point TP-8, and so on. The pressure or force ofthe touch event can be determined by measuring peak values of thesampled mixed signal. Thus, both the locations and forces of touchevents along the horizontal traces may be determined at touch points(TPs) that are between the vertical traces.

The resolution along the horizontal axis with which touch points may bedetected may vary for different implementations. According to someimplementations, the resolution may be very high with very preciselocations determined. Alternatively and according to a particular classof implementations, the resolution may be designed to be appropriate forparticular applications by quantizing the touch point locations. In suchimplementations, each horizontal trace may be thought of as a series ofsegments that each resolve to a particular touch point location alongthat trace. Quantization simplifies the detection of touch events byreducing the number of allowable locations to which the measured ratiosmap. For example, according to a particular implementation, there areonly three allowable locations for each vertical trace along aparticular horizontal trace; i.e., at the vertical trace itself and atlocations immediately to its left and right. This may be understood withreference to FIG. 16.

In the depicted example, touch points TP-1, TP-8, TP-9 and TP-10represent resolvable touch points along horizontal trace 1A. That is,any touch events falling along the segment of trace 1A within aparticular one of the touch point ovals is resolved to the center ofthat segment. Put another way, the determined ratio of the relativecontributions to the measured signal from primary detection signals S1and S2 corresponds to a particular touch point if that ratio fallswithin a range of values associated with that touch point, e.g., TP-8might correspond to values between 71/29 and 63/37. In this examplethen, each vertical trace may be used to detect 3 touch points alongeach horizontal trace, i.e., one at the trace and one on other side.

As will be appreciated, there may be situations in which the valuederived from the signal on any one vertical trace may be ambiguous. Forexample, a single touch point at TP-8 might be indistinguishable fromtwo simultaneous touch points at TP-1 and TP-9 if only the signal onvertical trace f is considered. Therefore, according to someimplementations, the processor can distinguish between these two caseswith reference to the values derived from signals on other verticaltraces that are close in time. In this example, the signal on verticaltrace g would be different for the single touch point case than it isfor the two touch points due to the proximity of touch point TP-9.

Thus, the processor can use multiple values derived from adjacentvertical traces to disambiguate among various scenarios. More generally,implementations are contemplated in which the processor is configured totake into account multiple data points (separated in space and/or time)in order to accurately and reliably discriminate between scenarios thatmight otherwise be ambiguous. Another example of a technique that may beemployed to disambiguate touch event scenarios involves connecting othervertical traces to a known potential (e.g., ground) when a particularvertical trace is being read (rather than leaving them floating). Asdiscussed above with reference to the implementations of FIGS. 15A and15B, this may reduce contributions from touch events associated with theother vertical traces. And as discussed in greater detail below,mechanical elements can be introduced that promote the quantization oftouch point locations and may serve to further promote disambiguation.

According to some implementations, ambiguity may also be dealt with bygenerating multiple values for each vertical trace signal while aparticular horizontal trace is energized. For example, horizontal trace1A may be energized with signal S1 applied via buss 1 and signal S2applied via buss A. Values are then successively generated by theprocessor for the signals received on vertical traces e-i. Horizontaltrace 1A may then be energized by reversing the two primary detectionsignals (signal S1 on buss A and signal S2 on buss 1) and generatinganother set of values for the signals on traces e-i. This second set ofvalues may be generated immediately following generation of the firstset of values, or on a successive loop through all of the horizontaltraces. As will be appreciated, this additional information may be usedby the processor for discriminating between potentially ambiguousscenarios. For example, for a touch event at a particular touch pointthe same ratio of signal contribution should be determined regardless ofthe trace ends to which signals S1 and S2 are applied. The duplicativedata may therefore be used to verify or validate the first data.Alternatively, the duplicate data values for a particular combination ofhorizontal and vertical trace could be averaged.

It should also be noted that the number and the size of touch pointsthat can be resolved by a single vertical trace may vary. For example,the size of the touch points may correspond to the size of the averagehuman fingertip. Alternatively, the size of the touch points maycorrespond to smaller instruments such as the tips of styluses orpointers. In addition, more than three touch points (e.g., 5 or 7) maybe resolved by each vertical trace. It should also be noted that thenumber of touch points that may be resolved may also be constrained bythe uniformity and consistency of the resistance of both thepiezoresistive material and the horizontal traces, i.e., the greater theuniformity and/or consistency of these components, the greater theresolution that may be supported. On the other hand, because the valuesbeing generated are ratios (at least for touch event locations), as longas the resistance of a horizontal trace is relatively consistent alongits length, there need not be a high level of consistency from onehorizontal trace to the next.

As will be appreciated with reference to the foregoing, the techniquesdescribed herein may result in a significant reduction in signal linesrequired to bring signals to and from the array relative to conventionalarrays of comparable resolution. However, as will also be appreciated,there may be scenarios in which multiple touch events occurring alongthe same vertical trace result in potentially ambiguous data. Forexample, touch events might occur simultaneously at touch points TP-1and TP-2 in FIG. 16. When horizontal trace 1A is energized and thesignal on vertical trace f is captured, there will be contributions tothe captured signal from both touch events. That is, the touch event attouch point TP-1 will result in contributions from primary detectionsignals S1 and S2 in the mixed signal on trace f as described above. Inaddition, because buss 1 is also driven by signal S1, there will be acontribution to the signal on trace f from the touch event at TP-2 alonghorizontal trace 1B. Similarly, when trace 1B is selected forenergizing, there will be contributions from both touch events in thatdata as well.

Therefore, according to some implementations, “ghost” detection signalsare introduced in the array simultaneous with the primary detectionsignals. These signals allow the processor to account for any unwantedcontributions from simultaneous events along the same vertical trace sothat it can generate an accurate representation of any touch eventsalong the primary horizontal trace being energized. The way in whichthis may be achieved may be understood with reference to FIGS. 16 and17.

In this example, the primary horizontal trace being energized withprimary detection signals S1 and S2 is trace 1A (i.e., the topmost tracein the figure), and the vertical trace for which a signal is beingcaptured is trace f. Because buss 1 must be active for trace 1A to beenergized, it is possible for unwanted contributions to the signal ontrace f from signal S1 to come from touch events at TP-2, TP-4 and TP-6.Similarly, because buss A must also be active, unwanted contributionsfrom signal S2 may result from touch events at TP-3, TP-5 and TP-7.

To account for the unwanted contribution from any touch event at TP-2,ghost detection signal S3 is introduced on buss B while trace 1A isenergized. As discussed above, a touch event at touch point TP-2 may berepresented by a ratio that represents the relative contributions ofsignals S1 and S3 at vertical trace f. Because this relationship isknown, i.e., 75/25, and because the magnitude of the contribution fromsignal S3 is also known (because it is measured in isolation), themagnitude of the contribution from signal S1 due to a touch event atTP-2 may be determined and accounted for when calculating the values fora touch event at or near TP-1. Similarly, to account for the unwantedcontribution from any touch event at TP-7, ghost detection signal S4 isintroduced on buss 2 (not simultaneous with signal S3 on buss B becausethat would energize trace 2B).

In the depicted example, signal S3 is a 2 kHz signal with a 50% dutycycle, and signal S4 is a 3 kHz signal also with a 50% duty cycle. Itwill be understood that these are merely representative examples andthat a wide range of alternatives may be employed for differentapplications; as long as the timing and amplitudes of the signals aresuch that the relative contributions of the various signals to aparticular mixed signal can be determined as described.

To account for unwanted contributions for all possible touch eventsalong vertical trace f while horizontal trace 1A is energized, ghostdetection signals S3 and S4 are successively introduced for each touchpoint along vertical trace f for which such a contribution might occur.Thus, signal S3 is introduced successively to busses B, C and D toaccount for touch points TP-2, TP-4 and TP-6, respectively; and signalS4 is introduced successively to busses 4, 3 and 2 to account for touchpoints TP-3, TP-5 and TP-7, respectively. Ghost detection signals areintroduced in a similar manner for each signal capture on verticaltraces e-i. And this is done for each horizontal trace. Those of skillin the art will understand how to extrapolate from the foregoingdiscussion to account for all possible combinations of multiple touchevents along any of the vertical traces.

As an alternative, instead of using two different ghost detectionsignals that are successively introduced, implementations arecontemplated in which a sufficient number of unique ghost detectionsignals are simultaneously introduced. As another alternative, a singleghost detection signal can be introduced sequentially to all of therelevant busses (assuming the far side of the buss is grounded). In suchimplementations, the magnitude of the detected ghost signal would bestored while the ground and ghost detection signal are exchanged so thatthe ratio can then be computed.

Returning to the example in which horizontal trace 1A is energized, onceall contributions to the signal on vertical trace f from other possibletouch points along the vertical trace are identified, the unwantedcontributions may be removed (e.g., subtracted) from the value beingdetermined so that the horizontal position of any touch event alongtrace 1A (if any) may be determined from the resulting ratio asdescribed above.

As each successive horizontal trace is energized, a pair of values isgenerated for each combination of an energized trace with each of thevertical traces. One value in the pair represents the relativecontributions of the primary detection signals to the signal received onthe vertical trace (e.g., expressed as a ratio), and the other theamplitude or magnitude of that signal (e.g., expressed as a value thatis proportional to the force of the touch event; at least within thedynamic range of the piezoresistive material). In the example of array1600 of FIG. 16, a single pass through the array would result in a dataset having 80 pairs of such values, i.e., 5 pairs of values for each of16 horizontal traces. Each of these pairs of values may or may notrepresent a touch event. The ways in which the data may be processed todetermine whether or not a pair of values represents a meaningful event,i.e., a touch event, may vary considerably.

For example, in some implementations, a pair of values may be considereda touch event if the amplitude or magnitude value for the pair (e.g., apeak measurement of the received signal) exceeds a threshold. Thethreshold may be fixed or dynamic. For example, the threshold might bedetermined using an average of the amplitude measurements made acrossthe array over a given time period (e.g., corresponding to a single passthrough the array). If the amplitude value for a given pair of valuesexceeds the threshold, the pair of values is considered to represent atouch event, and the location of the touch event is determined withreference to the ratio value of the pair (e.g., mapped to a quantizedtouch point as discussed above).

According to some implementations, the reliability with which touchevents are detected may be enhanced by comparing the data sets generatedby successive passes or “scans” through the array over time. A scancorresponds to energizing each of the horizontal traces once and readingsignals from each of the vertical traces once for each horizontal trace.For a particular implementation of the example of FIG. 16, 5 signalreads (corresponding to vertical traces e-i) may occur for each of the16 horizontal traces each scan. As discussed above, this results in 10values for each horizontal trace; 5 ratios representing the relativecontributions of signals S1 and S2 and 5 amplitudes representing theforce of any touch events. Each set of 160 values may be thought of as a“frame” of data that may be compared to one or more previous and/orsubsequent frames for the purpose of more accurately and reliablydetecting touch events. This is illustrated in FIG. 20 in which 7successive frames of data are represented.

According to some implementations, techniques developed for theprocessing of frames of video may be adapted to make detection of touchevents more robust and reliable. For example, the primary and ghostdetection signals described above with reference to FIG. 16 may bethought of like the RGB color components of a video frame with thestrengths of the respective signals being analogous to the strengths ofthe RGB contributions. A frame could be saved each time the two primarydetection signals are changed to a new resistive trace or reversed andfor each iteration of the ghost detection signal states.

With such data methods of processing image data (e.g., for machinevision) would be applicable. Such methods often use versions of waveletanalysis to decompose a video frame. Because of the known constraints ofour data (array size, time series) simplified forms of wavelet analysismay be suitable, making it possible to go readily from our input valuesto a simplified post analysis result.

According to some implementations, machine learning techniques may beemployed that use of Markov chains or similar mechanisms to trackchanges over time. Markov modeling is regularly used to compare presentstates to previous states, providing specific classifications of thechain. Some implementations may use edge detection along withstatistical approaches such as Bayesian methods to analyze data. Becauseof the highly constrained data sets that may be produced with someimplementations, tools from the realm of video analysis lend themselvesto robust solutions.

For additional information about signal processing techniques that maybe adapted for use with implementations described herein please refer to(1) Machine Learning for Multimodal Interaction: First InternationalWorkshop; MLMI 2004, Martigny, Switzerland, Jun. 21-23, 2004, RevisedSelected Papers (Google eBook); (2) Automatic Video Object SegmentationUsing Wavelet Transform and Moving Edge Detection; Xiao-Yan Zhang andRong-Chun Zhao; 2006 International Conference on Machine Learning andCybernetics, 13-16 (August 2006); (3) Human detection based on discreteWavelet transform; M. M. Deshpande, J. G. Rana, and M. M. Pawar; IETChennai 3rd International on Sustainable Energy and Intelligent Systems(SEISCON 2012) (27-29 Dec. 2012); (4) Wavelet-based Image CompressionUsing Support Vector Machine Learning and Encoding Techniques; RakibAhmed; Proceedings of the 8th IASTED International Conference onComputer Graphics and Imaging (2005); (5) Video Forensics in TemporalDomain using Machine Learning Techniques; Sunil Jaiswal and SunitaDhavale; I. J. Computer Network and Information Security (July 2013);(6) Content Based Image Classification with Wavelet Relevance VectorMachines; Arvind Tolambiya, S. Venkataraman, Prem K. Kalra; SoftComputing—A Fusion of Foundations, Methodologies andApplications—Special Issue on Pattern Recognition and InformationProcessing Using Neural Networks; Volume 14 Issue 2, (September 2009);and (7) What to believe: Bayesian methods for data analysis; John K.Kruschke; Trends in cognitive sciences, Volume 14, Issue 7 (July 2007).The entire disclosure of each of the foregoing is incorporated herein byreference for all purposes.

Depending on the application, and in particular for implementations inwhich traces are formed on a flexible piezoresistive substrate, someform of mechanical and/or environmental protection may be desirable. Forexample, thin silicone sheets could be laminated over one or both sidesof the array.

According to various implementations, the quantization of touch pointsmay be promoted by introducing mechanical structures in and around thearray that effectively focus forces on the array toward the desireddiscrete locations. And as will be discussed, some of these structuresmay also be useful for optimizing an array for different ranges ofapplied force, providing mechanical support, promoting alignment ofsystem components, and/or providing environmental protection. Examplesof such structures will be discussed with reference to FIGS. 18 and 19.

FIG. 18 shows a section of a two-dimensional sensor array 1800 in whichvarious mechanical features are shown in different regions of the arrayfor the purpose of illustration. The depicted features include forcefocusing elements (e.g., bumps 1802), structural elements (e.g., posts1804) and apertures (e.g., cutouts 1806). Bumps 1802 are illustrated bythemselves in region 1808. Posts 1804 are illustrated by themselves inregion 1810. Bumps 1802 and posts 1804 are shown used together in region1812. Cutouts 1806 are shown alone in region 1814 and in combinationwith bumps 1802 in region 1816. As will be appreciated, these regionsare merely for illustration and that implementations are contemplated inwhich some or all of the features are used in various combinations.

According to a particular implementation and as illustrated incross-sectional view A-A of FIG. 19, bumps 1802 may be convex featuresthat are formed on or part of a molded silicone sheet 1902 that isaligned with and laminated to piezoresistive material 1904. In somecases, silicone sheet 1902 may form part of an enclosure that providesenvironmental protection to the enclosed components. In the depictedimplementation, bumps 1802 are on the side of material away from theconductive traces and are aligned with the array's quantized touchpoints (e.g., TP-1 through TP-10 of FIG. 16), acting to focus force 1906applied to the top of the array to those touch points. Alternatively,bumps 1802 may be formed on some other type of substrate (e.g., a rigidsubstrate like a printed circuit board). Bumps may also be formed in thepiezoresistive material itself by shaping of the material at the desiredlocations. This may be accomplished by, for example, forming the bumpsinto the fabric when it is made or by embossing the features into thefabric. In another alternative, the bumps may be formed on a backingsheet to which the piezoresistive material is secured (e.g., laminated).Other variations apparent to those of skill in the art are within thescope of this disclosure. In addition, a wide variation in quantizationand response (e.g., dynamic range) may be achieved by varying the size,height, spacing and flexibility of bumps 1802.

Posts 1804 extend through piezoresistive material 1904 as shown in crosssection view B-B of FIG. 19 and may serve multiple purposes. Forexample, posts 1804 may serve to keep the array components aligned. Thismay be particularly important where posts 1804 are used in conjunctionwith bumps 1802 as shown in region 1812 of FIG. 18. Not only would suchan arrangement serve to maintain alignment of bumps 1802 with thedesired quantized touch points, posts 1804 may also serve to promotequantization by deflecting force laterally toward adjacent bumps 1802.In addition, the substrate from which posts 1804 extend may form part ofan enclosure that provides environmental protection to the enclosedcomponents.

According to some implementations, posts 1804 may not extend all of theway through piezoresistive material 1904 (i.e., being only secured toone of the substrates on either side of material 1904). This wouldmitigate the scenario in which a touch event occurs directly over apost. In such a scenario, if the post is rigid and extended all the waythrough the piezoresistive material, the touch event might not register.By contrast, if the post extended only part of the way through thepiezoresistive material, a touch event over the post would result insome deflection that would transfer force to the piezoresistivematerial.

As an alternative and as depicted in FIG. 19, posts 1804 may extend allof the way through piezoresistive material 1904. In suchimplementations, posts 1804 may be constructed from a flexible material(e.g., silicone) so they compress with touch events. Posts 1804 mightalso be secured to both substrates on either side of the piezoresistivematerial. Such a configuration might be important, for example, inapplications in which lateral shearing forces (e.g., force 1908) areexpected on the surface of the array. In such applications, securing ofthe posts in this way would ensure that alignment is maintained in thepresence of such shearing forces. Posts 1804 may also be tapered topromote some level of compression. More generally, the geometry (taper,thickness, etc.), flexibility, and spacing of posts 1804 may becontrolled to achieve a desired array response.

Cutouts 1806 may be introduced in the piezoresistive material to promoteisolation and inhibit cross-talk between conductive traces. This willimprove the signal-to-noise ratio for the signals being read from thevertical traces and thereby improve overall system performance. And aswill be appreciated, this may also serve to promote the quantization oftouch point locations. And some implementations may take advantage ofthe absence of the piezoresistive material at the cutouts by includingposts that are aligned with the cutouts. These may be like posts 1804 ormay conform more closely to the shape of the cutout. For example, theposts could fill the cutout. As will be appreciated, such an approachwould serve to provide mechanical structure, promote alignment, and/orpromote a desired dynamic range.

As mentioned above, implementations enabled by this disclosure may besuitable for a broad range of applications. That is, two-dimensionalsensor arrays as described herein may be useful in any context in whichit is important or desirable to monitor the locations and magnitudes offorces on a surface at a point in time or over a period of time. In oneexample, such a two-dimensional array might be integrated in athleticfootwear to monitor technique or track stress. In another example, ayoga mat might include such a two-dimensional array for the purpose ofmonitoring and/or teaching proper technique. In another example, thefloor of an elder-care facility might include such arrays to indicatethat a patient has fallen. In yet another example, an array might beintegrated in the seat of an office chair to promote ergonomically soundposture. In still another example, a two-dimensional array might beincorporated in a mattress or pad for use in an infant's crib orbassinet. Such an array would be useful for monitoring an infant'ssleeping position and to trigger an alarm when, for example, thesleeping position is determined to represent a high risk for suddeninfant death syndrome (SIDS). As will be understood from the diversityof these examples, the potential applications of two-dimensional sensorarrays implemented as described herein are virtually limitless.

It will be understood by those skilled in the art that changes in theform and details of the implementations described herein may be madewithout departing from the scope of this disclosure. In addition,although various advantages and aspects have been described withreference to various implementations, the scope of this disclosureshould not be limited by reference to such advantages and aspects.Rather, the scope of this disclosure should be determined with referenceto the appended claims.

1. A sensor system, comprising: piezoresistive fabric; a flexibledielectric substrate having a plurality of conductive trace groupsformed on a first side of the flexible dielectric substrate and aplurality of routing traces formed on a second side of the flexibledielectric substrate opposite the first side, the conductive tracegroups and the piezoresistive fabric forming a sensor array in whicheach of the conductive trace groups corresponds to a sensor in thesensor array, each of the conductive trace groups including twoconductive traces having complementary shapes, each of the conductivetraces being electrically connected through the flexible dielectricsubstrate to a corresponding routing trace on the second side of theflexible dielectric substrate; and sensor circuitry configured to usethe routing traces to energize the conductive trace groups and receiveresulting sensor signals, the sensor circuitry also being configured touse the sensor signals to generate data representing locations andmagnitudes of force resulting from objects in contact with a surface ofthe sensor system.
 2. The sensor system of claim 1, wherein the sensorcircuitry is further configured to generate successive frames of thedata for the sensor array, and to compare the successive frames of thedata to improve reliability of the data.
 3. (canceled)
 4. The sensorsystem of claim 1, wherein the complementary shapes of each conductivetrace group comprise interdigitated extensions of the two conductivetraces of the conductive trace group.
 5. The sensor system of claim 1,wherein the complementary shapes of each conductive trace group compriseclover and cruciform shapes.
 6. (canceled)
 7. The sensor system of claim1, wherein the piezoresistive fabric is a calendared material.
 8. Thesensor system of claim 7, wherein the piezoresistive material includespolymerized conductive particles.
 9. The sensor system of claim 1,wherein one or more characteristics of the conductive trace groups areconfigured to achieve a particular dynamic range for the sensor system,the one or more characteristics including one or more of (1) shapes ofthe conductive traces of each conductive trace group, (2) distancesbetween the conductive traces of each conductive trace group, or (3)conductivity of the conductive traces of each conductive trace group.10. The sensor system of claim 1, further comprising one or more of (1)force focusing elements configured to focus the force on the surface ofthe sensor system toward one or more corresponding sensors of the sensorarray, (2) structural elements configured to resist the force on thesurface of the sensor system, or (3) cutouts in the piezoresistivefabric that promote physical and electrical isolation of adjacentsensors. 11-20. (canceled)
 21. The sensor system of claim 1, wherein theconductive traces of each conductive trace group are electricallyconnected to the corresponding routing traces using conductive ink vias,conductive paint vias, metal vias, or metal rivets.
 22. The sensorsystem of claim 1, wherein the piezoresistive fabric is a singlesubstrate for all of the conductive trace groups.
 23. The sensor systemof claim 22, further comprising an insulating layer adjacent thepiezoresistive fabric, the insulating layer having openings that line upwith the conductive trace groups.
 24. The sensor system of claim 1,wherein the piezoresistive fabric is multiple pieces, each piece ofpiezoresistive fabric corresponding to a different subset of theconductive trace groups.
 25. The sensor system of claim 1, wherein thepiezoresistive fabric is coupled to the flexible dielectric substrate.26. The sensor system of claim 25, wherein the piezoresistive fabric islaminated to the flexible dielectric substrate.
 27. The sensor system ofclaim 1, wherein the piezoresistive fabric is held at a distance fromthe conductive trace groups when pressure is not applied to the surfaceof the sensor system.
 28. The sensor system of claim 1, wherein theconductive traces of the conductive trace groups and the routing tracesare conductive ink printed on the first and second sides of the flexibledielectric substrate.
 29. The sensor system of claim 28, furthercomprising an insulating material printed at intersections of therouting traces that insulate the intersecting routing traces from eachother.
 30. The sensor system of claim 1, wherein the sensor circuitry isconfigured to energize the conductive trace groups in a sequence and toreceive the sensor signals in the sequence, and wherein the sensorcircuitry is further configured to use the sensor signals to determine aspeed of motion of a touch event relative to the surface of the sensorsystem, and a direction of motion of the touch event.
 31. The sensorsystem of claim 1, wherein the sensor array is one of a linear array, arectilinear array, a polar array, a hemispherical array, or an irregulartwo-dimensional array.